JPS6018011A - Automatic gain control amplifying stage - Google Patents

Abstract

PURPOSE:To secure a stable operation for gain control regardless of the output level by setting a gain controller between an output stage and a detecting circuit to keep the signal impressed to the detecting circuit at a fixed level. CONSTITUTION:Signal amplifying stages AMP1-AMP5 are connected to each other in cascade via variable attenuators ATT1-ATT4. The output of the AMP5 is supplied to a detecting circuit DT via a variable resistor RV1 which controls the gain and an AMP6. The output of the DT is supplied to a control circuit CTL via a DC amplifier DCA. The circuit CTL controls attenuators ATT1-ATT5 and keeps the output of the AMP5 at a prescribed level. For instance, the gain of lthe AMP6 is increased to set the input to the DT at about the same level as the conventional input in case the output of the AMP5 is set at a level lower than the convertional input. Since the input level of DT is kept at a fixed level the automatic gain control is possible with stability by the circuit CTL regardless of the output level of the AMM5.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to an automatic gain control amplification stage that operates stably without significantly changing the amplification stage configuration even when the output signal level is varied.

(2) Prior Art and Problems The configuration shown in FIG. 1 as a feedback type automatic gain control amplifier stage is well known. That is, the signal amplification stages AMP1 to AMP
5 are cascade-connected between each stage via variable attenuators AT'F1 to ATT4. The output of the amplifier AMP5 drives the control circuit CTL via the detection circuit DT and the DC amplifiers DC, A, and the output of the control circuit CTL controls the variable attenuator to maintain the output of the 8MP5 at a predetermined value. In recent years, the use of digital systems for wireless communication has been put into practical use, and at that time, an amplification stage with a large change in the output level of an automatic gain control stage in the same equipment, such as +5 dB or -10 dB, was called a. In some cases, it would be wasteful to design the amplifier stage separately (11, 1), so it is necessary to adjust the standard output voltage by adjusting the variable attenuator or changing the control reference potential in the control circuit CT L. The adjustment was complicated.Also, due to the temperature characteristics of the diode used in the detection circuit DT, it became impossible to perform the specified automatic gain control.As shown in Figure 2. The characteristic of the voltage V vs. current f of the diode is approximately a square curve, so when this characteristic curve moves left and right due to temperature changes, the change in I with respect to the change in ■ will have a large effect when ■ is small. That is, when the output level is set to a small value, there is a drawback that when a temperature rise occurs, the control operation is performed as if the output level were to be increased.

(3) Purpose of the Invention The purpose of the present invention is to improve the above-mentioned drawbacks, and to provide an automatic gain control amplification stage that operates stably even when the output level is set to various values without significantly changing the amplification stage configuration. There is a particular thing.

(4) Structure of the Invention The structure of the present invention to achieve the above-mentioned object is that, in an amplification stage that performs automatic gain control by feeding back a signal from the output stage to the previous stage via the detection circuit, the output stage and the detection circuit are connected to each other. In between, a gain controller was inserted to stabilize the level of the signal applied to the detection circuit.

(5) Embodiment of the Invention FIG. 3 is a block diagram showing the configuration of an embodiment of the invention. The same reference numerals as in FIG. 1 indicate similar parts. Third
In the figure, AMP6 is an amplifier having a built-in feedback circuit like an operational amplifier, and is inserted between the output stage amplifier AMP5 and the detection circuit so as to amplify the signal applied to the detection circuit DT.

RV is a variable resistor that changes the input impedance of the amplifier AMP6. The gain of the amplifier AMP6, that is, the level of the signal applied to the detection circuit, can be changed by adjusting the variable resistor RV. Therefore, when the output level of the amplifier type MP5 is set to a standard value lower than before, for example, the output level of the amplifier AM
The gain IM of P6 is increased and the input level to the detection circuit DT is controlled to be approximately the same value as before. Therefore, the output of the control circuit CTL can be set to a value that is not affected by temperature changes, so that the attenuator ATT can be controlled accurately.

(6) Effects of the Invention In this way, according to the present invention, the operation of the detection circuit can be stabilized and accurate, so even when the output level of the automatic gain control stage is set to a different value, especially a small level, the gain control It works better. Also, it is possible to share the amplification stage, making the equipment cheaper. It has an effect of 1lli.

[Brief explanation of drawings]

Figure 1 is a diagram showing the configuration of a conventional automatic gain control amplifier stage, Figure 2 is a diagram explaining the diode characteristics of the detection circuit in Figure 1, and Figure 3 is a diagram showing the configuration of an embodiment of the present invention.・It is a Tsuku diagram. AMPI to AMP5 - Signal amplification stages ATTI to ATT4 - - Variable attenuator 1) T - Detection circuit D CA - DC amplifier CTL - Control circuit AMP6 - Gain controlled amplifier Rv - Variable resistor Patent applicant Fujitsu Co., Ltd. Company agent Patent attorney Eisuke Suzuki

Claims (1)

[Claims] In an amplification stage that performs automatic gain control by feeding back a signal from the output stage to the previous stage via a detection circuit, a gain controller is inserted between the output stage and the detection circuit to constantize the level of the signal applied to the detection circuit. An automatic gain control amplification stage featuring a stop.